This application is based on application No. 101363 filed in Japan on Mar. 30, 2001, the content of which incorporated hereinto by reference.
This invention relates to a battery pack containing a circuit breaker which cuts-off current flow if excessive current flows through the batteries or if battery temperature rises abnormally.
A battery pack containing a circuit breaker protects the batteries by cutting-off the current when excessive current flows through the batteries or when battery temperature rises abnormally. There are two types of circuit breakers. There are circuit breakers which switch on and off via movable contacts, and there are circuit breakers which abruptly change electrical resistance with temperature such as PTC devices. A movable contact circuit breaker contains a bimetal element which heats as a result of current flow. The bimetal element is heated by current flow induced Joule-heating and switches the movable contact from the on to off position to cut-off current flow. A PTC device abruptly increases its electrical resistance when temperature rises to almost eliminate current flow.
FIG. 1 shows a battery pack containing a circuit breaker 4. In the battery pack shown in this figure, circuit breaker 204 leads 2026 are connected to the batteries 201. The circuit breaker 204 is disposed in close proximity to battery surfaces for quick current shut-off. Insulating sheet 2027 is disposed between the circuit breaker 204 and the batteries 201 to prevent short circuit caused by a lead 2026, from the closely positioned circuit breaker 204, touching a battery 201.
To accurately position the circuit breaker 204 in a battery pack with circuit breaker 204 leads 2026 connected to the batteries 201 as shown in FIG. 1, extra effort is required during assembly. Further, this system has the drawback that the circuit breaker 204 can easily be out of position. Circuit breaker position affects its current shut-off characteristics. This is because the circuit breaker is heated by battery current flow as well as by heat from the batteries. If the circuit breaker is further away from the batteries, heat conduction from the batteries to the circuit breaker is reduced and turning the circuit breaker off becomes more difficult. In contrast, if the circuit breaker is closer to the batteries, heat conduction improves and the circuit breaker is more easily turned off. Therefore, the relative position of the circuit breaker and the batteries changes circuit breaker current shut-off characteristics. It is required that circuit breaker characteristics show reliable current shut-off at preset conditions. Realization of an ideal battery pack is impossible if circuit breaker cut-off action is either too slow or too fast. If circuit breaker shut-off is too slow, batteries cannot be sufficiently protected, battery characteristics can degrade, and battery internal pressure can become abnormally high. In contrast, if circuit breaker shut-off is too fast, the battery pack cannot be used under conditions which should allow battery pack use.
The present invention was developed to eliminate the drawbacks described above. Thus it is a primary object of the present invention to provide a battery pack allowing accurate circuit breaker positioning along with ease of assembly thereby resulting in precise circuit breaker action, effective battery protection, and safe operation.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The battery pack of the present invention is provided with a case, batteries housed inside the case, a printed circuit board, and a circuit breaker. Battery protection circuit components are mounted on the printed circuit board. The circuit breaker is connected in series with the batteries and switches off to protect the batteries if excessive current flows through the batteries or if battery temperature rises above a set temperature. The circuit breaker has a plurality of solder terminals attached to the circuit breaker casing. One, or a plurality of the solder terminals are attached to the printed circuit board by solder re-flow. The printed circuit board is connected to the batteries via leads and is also disposed in a fixed position inside the case. The circuit breaker mounts in a fixed position inside the case via the printed circuit board.
This battery pack configuration has the characteristic that assembly is simplified and the circuit breaker can be disposed at a precise position. This is because circuit breaker solder terminals are attached to the printed circuit board by solder re-flow, and the printed circuit board is disposed in a fixed position. This system of solder re-flow attachment of circuit breaker solder terminals to the printed circuit board has the characteristic that manufacturing complexity is avoided and simplification is possible. Further, since the printed circuit board, with circuit breaker attached, is connected to the batteries via leads and disposed in a fixed position, the circuit breaker, which is positioned via the printed circuit board, can always maintain a consistent position relative to the batteries and can be disposed in an ideal location. In this fashion, a battery pack, in which the circuit breaker can always be disposed at a precise location, increases circuit breaker thermal sensitivity, allows accurate circuit breaker operation, and effectively protects the batteries to allow safe operation.
The circuit breaker preferably has solder terminals at both ends of its casing, and those solder terminals are firmly attached to the printed circuit board by solder re-flow. In addition, the circuit breaker may have a solder terminal and a lead attached to its casing. The solder terminal can be re-flow soldered to the printed circuit board for attachment and the lead can be connected to a battery electrode. A circuit breaker type containing a current cut-off contact which switches from on to off with excessive current or temperature can be used for this circuit breaker.
The printed circuit board is preferably disposed in a fixed position facing the surfaces of the batteries and providing a gap between the batteries and the printed circuit board for the circuit breaker. The circuit breaker can be mounted within this gap. Further, the circuit breaker can be disposed to put the surface of its casing in close proximity to the surfaces of the batteries. In particular, the circuit breaker can be disposed in direct contact with the surfaces of the batteries. The printed circuit board can be mounted via a holder in a fixed position relative to the surfaces of the batteries.
FIG. 1 is an abbreviated cross-section view of a related art battery pack containing a circuit breaker.
FIG. 2 is an abbreviated cross-section view of an embodiment of a battery pack of the present invention.
FIG. 3 is an abbreviated cross-section view of another embodiment of a battery pack of the present invention.
FIG. 4 is a cross-section view showing one embodiment of a circuit breaker housed inside a battery pack.
FIG. 5 is a cross-section view showing another embodiment of a circuit breaker housed inside a battery pack.
FIG. 6 is a cross-section view showing another embodiment of a circuit breaker housed inside a battery pack.
FIG. 7 is a cross-section view showing another embodiment of a circuit breaker housed inside a battery pack.
FIG. 8 is a cross-section and plan view showing another embodiment of a circuit breaker housed inside a battery pack.
FIG. 9 is a cross-section and plan view showing another embodiment of a circuit breaker housed inside a battery pack.
FIG. 10 is a cross-section view showing another embodiment of a circuit breaker housed inside a battery pack.
FIG. 11 is a plan view showing the internal structure of the circuit breaker shown in FIG. 10.
FIG. 12 is a cross-section view showing another embodiment of a circuit breaker housed inside a battery pack.
FIG. 13 is a cross-section view showing one embodiment of a battery pack containing the circuit breaker shown in FIG. 6.
FIG. 14 is a cross-section view showing another embodiment of a battery pack containing the circuit breaker shown in FIG. 6.
FIG. 15 is a circuit diagram showing one embodiment of a battery pack containing the circuit breaker shown in FIG. 8.
FIG. 16 is a circuit diagram showing one embodiment of a battery pack containing the circuit breaker shown in FIG. 10.
FIG. 17 is an oblique view of another embodiment of a battery pack of the present invention.
FIG. 18 is an exploded oblique view of the battery pack shown in FIG. 17 as seen from below.